This disclosure relates generally to photodisruption induced by a pulsed laser beam and to the location of the photodisruption for treating a material, such as eye tissue. Although specific reference is made to cutting tissue for surgery such as eye surgery, the embodiments described herein can be used in many ways and with many materials to treat one or more materials, including cutting optically transparent materials.
Materials can be cut mechanically with chisels, knives, scalpels, as well as other manual surgical tools such as microkeratomes. In at least some instances, however, prior cutting methods and apparatuses can be less than desirable and provide less than ideal results. Further, at least some prior methods and apparatus for cutting tissue may yield a rougher surface than would be ideal. Materials, including tissue, can be also cut with laser beams. A surgical laser beam is preferred over manual tools like microkeratomes as it can be focused accurately on extremely small amounts of tissue, thereby enhancing precision and reliability.
Surgical lasers have been used in ophthalmology for a while now, and are used to cut eye tissue such as the cornea, the capsular bag, and the crystalline lens of the eye. For example, in the commonly-known LASIK (laser-assisted in situ keratomileusis) procedure, an ultra-short pulsed laser is used to cut a corneal flap to expose the corneal stroma for photoablation with an excimer laser so as to correct a refractive condition, such as myopia, hyperopia, or astigmatism. Ultra-short pulsed lasers emit radiation with pulse durations as short as 10 femtoseconds and as long as 3 nanoseconds, and a wavelength between 300 nm and 3000 nm. Excimer lasers produce radiation in the ultraviolet range. Besides cutting corneal flaps, ultra-short pulsed lasers are used in cataract surgery.
During laser cataract surgery, ultra-short pulsed lasers are used for cutting eye tissue such as the cornea and the capsular bag to gain access to the cataractous lens. The laser is also used to cut the cataractous lens so as to soften and/or fragment the cataract before removal. Indeed, conventional ultra-short pulse laser systems have been used to treat many patients. In some instances, however, these systems provide less than ideal results. For example, sometimes, when a corneal refractive treatment is combined with a lens treatment, such as the removal of the lens cortex and nucleus from the eye, the alignment of the eye with the laser surgery system can be less than ideal,
Ultra-short pulsed lasers are also used for corneal resection to prepare tissue for grafting. Prior methods and apparatuses for resecting corneal tissue for grafting purposes can also be less than ideal, meaning that fewer patients may receive the benefits of successful grafting procedures. Hence, it would be helpful to provide improved methods for resecting and grafting eye tissue to treat various eye diseases.
Many patients may have less than ideal optics of the eye. Some patients may have one or more refractive errors of the eye, such as myopia or hyperopia that can be corrected with spectacles, contact lenses, or the LASIK procedure. Patients may also have an irregularity of the cornea such as irregular astigmatism or corneal scarring. In at least some instances, these irregularities may not be easily corrected using prior surgical approaches. Among others, prior approaches to treating diseased cornea have included keratoplasty, such as penetrating keratoplasty (hereinafter “PK”). PK can sometimes result in less than ideal patient outcomes wherein the patient has less than ideal visual acuity following the procedure.
With some disease conditions, it can be helpful to replace a portion of the cornea instead of surgically penetrating it as is done in PK. For example, replacing a portion of the cornea may be helpful where the irregularity of the eye is related to a disease or a condition, including for instance, where low endothelial cell counts cause less than ideal optics of the cornea.
But, sometimes, prior methods and apparatuses to replace a diseased endothelium layer of the cornea can be less than ideal. One such approach, Descemet's membrane endothelial keratoplasty (“DMEK”), removes the endothelium and the underlying Descemet's membrane and replaces the diseased tissues with graft tissue from a donor. In other words, the endothelial layer and the Descemet's membrane is removed from the diseased eye and replaced with a healthy Descemet's membrane and endothelial cells from a donor eye. Unfortunately, the DMEK procedure can provide less than ideal outcomes in that some patients may not fully recover vision. DMEK can also be time-consuming and more complex than desired. Recently, another method that automates at least a portion of the DMEK procedure, referred to as Descemet's membrane automated endothelial keratoplasty (“DMAEK”) has been used. Although corneal surgeons may find DMAEK potentially less complicated to perform, the results of DMAEK can be less than ideal as following the procedure, some patients' vision may not be fully correctable to twenty/twenty (metric six/six), or even twenty/forty (metric six/twelve).
Hence, it would be desirable to provide improved methods and apparatuses that overcome at least some of the limitations and disadvantages of prior systems and methods.